The communications between a mobile terminal and a serving cell, such as the uplink communications from the mobile terminal to the serving cell, may sometimes affect resource utilization, throughput, latency and coverage. To enhance uplink communications improvements, the ongoing evolution of wireless communications systems such as, for example the enhanced dedicated channel (E-DCH) in cell Forward Access Channel (FACH) (CELL_FACH) state feature was introduced into wireless standard specifications, such as the third generation partnership project (3GGP) Release 8 specifications.
Mobile terminals operating in a CELL_FACH mode may use a contention based E-DCH channel for uplink (UL) transmission rather than a traditional random access channel (RACH). The contention-based E-DCH channel allows for mobile terminals to transfer signaling and data at significantly higher data rates and for longer durations, which reduces transfer and state transition delays.
Support for concurrent deployment of transmission time interval (TTI) settings, (e.g., 2 ms and 10 ms), will be allowed for the common E-DCH in the CELL_FACH state in 3GGP Release 11 (Rel-11). In this regard, 3GGP Rel-11 supports concurrent deployment of 2 ms and 10 ms TTI settings in a cell. A single TTI setting, which may be determined and broadcast by a communications network, may be used by mobile terminals accessing the E-DCH in the CELL_FACH state within a particular cell. Additionally, for example, 3GPP Release 11 compliant mobile terminals may utilize 2 ms TTIs and 10 ms TTIs in a cell. While a smaller TTI, such as the 2 ms TTI, may be more advantageous from fast scheduling and latency standpoints, a larger TTI, such as the 10 ms TTI, may be more widely utilized by mobile terminals in a cell to reliably transfer signaling and data to the network, particularly in coverage limited scenarios. For instance, some 3GPP Release 8 (Rel-8) legacy mobile terminals may be able to utilize the 10 ms TTI but are typically unable to communicate via the 2 ms TTI. Since some mobile terminals of a cell may be able to utilize both the 2 ms and 10 ms TTIs, while other mobile terminals may only be able to utilize the 10 ms TTI, the network may need an efficient mechanism of communicating resources to the mobile terminals of a cell.
A number of mechanisms to enable a network to communicate resources to mobile terminals capable of supporting different TTIs have been proposed, however these mechanisms suffer from drawbacks. One approach for a network to communicate with mobile terminals capable of supporting different TTIs, involves a network splitting a physical random access channel (PRACH) signature space between legacy devices such as, for example, R99 and Rel-8 mobile terminals (e.g., utilizing 10 ms E-DCH TTI signatures and/or R99 PRACH signatures) that are capable of utilizing a 10 ms TTI and a signature space (e.g., utilizing 2 ms TTI signatures) for Rel-11 mobile terminals capable of using a 2 ms TTI and a 10 ms TTI. However, a drawback of this approach is that the signature space is limited which makes it difficult to allocate sufficient resources for a highly loaded cell. In this regard, utilizing this approach may be difficult to achieve an optimum balance between 10 ms TTI signatures (or resources) and 2 ms TTIs signatures to achieve the best resource utilization, quality of service and capacity.
Another approach that suffers from drawbacks involves a network utilizing a PRACH scrambling code to communicate 10 ms TTI signatures for legacy devices and an additional PRACH scrambling code for transmission of 2 ms TTI signatures to Rel-11 compliant mobile terminals in order to split the signatures for E-DCH transmission. Although this approach may be used to separate the traffic between Rel-11 compliant mobile terminals and legacy mobile terminals and may increase the signature space, additional signaling overhead on an already limited broadcast channel may be required, which may complicate an initial access procedure and may result in the network needing to schedule the system information differently which may impact the performance of all devices of the cell.
Another approach for a network to communicate resources to mobile terminals utilizing different TTIs involves the network signaling a TTI using a set of signatures that may refer to the same/first PRACH scrambling code (e.g., a PRACH scrambling code used for signatures of R99 and Rel-8 legacy devices), or it may refer to another/second scrambling code. However, this approach typically requires a new set of signatures to be defined to differentiate the Rel-11 compliant mobile terminals from legacy devices (e.g., R99 mobile terminals, Rel-8 mobile terminals). Moreover, an additional parameter is typically needed to identify the TTI utilized by each mobile terminal. By utilizing this approach, Rel-11 complaint mobile terminals may need to send a preamble on a new scrambling code and may indicate a signature corresponding to either the first or the second scrambling code. A drawback of this approach is that it typically introduces additional signaling overhead on a broadcast channel and may complicate the initial access procedure between the network and mobile terminals in a cell.
In view of the foregoing drawbacks, a more reliable and efficient manner of communicating resources to mobile terminals utilizing different capabilities may be beneficial.